In the field of carpentry accessories, there are complex and unwieldy devices intended to help in one way or another to establish right angles and miter cuts, spaced parallel cuts, and so forth. Some of these are designed to replace existing, simpler structures, and others add additional tools that must be and carried on-site by the carpenter. A tool must be simple, lightweight and compact to be accepted by the trade since the tradesman can already do anything he needs to do, with the tools he already has. Tools that replace an existing tool and eliminate one or more small inconvenience from the job without adding pounds or cubic inches to the tool mass, have a chance of success.
One such minor annoyance arises when one needs to cut off an orthogonal length of a plank. Traditionally the way this is done is by laying the flat carpenter's square on the plank with one leg along the length of the board and the other leg laying across the board, and making a transverse pencil line across the whole run of the cut-off path. Then a saw, usually the hand-held circular saw used extensively by framing carpenters and the like, is used to follow the line across the board.
The line is often difficult to follow as it may not have been well lit in the first place, and continued sawdust accumulation along the cut line, and vibration, obscure the pencil mark. The saw blade safety cover also obstructs the cut line, making it difficult to see either the pencil line or the blade at its intersection with the board, and hard to be sure the blade path is true to the line. This results in undercuts, overcuts, and angled cuts that were supposed to have been orthogonal. On outdoor jobs which rely on sunshine for light, as dusk approaches the mistakes proliferate. It becomes increasingly difficult to insure the alignment of the rotating blade and the pencil mark in the flurry of sawdust under the spring-loaded blade guard.
Because right angularity is built into the carpenter's saw, and the distance between the sole plate of the saw and the plane of the blade is constant, one would think that there would be a more efficient way of making such saw cuts, and in fact the prior art has developed several devices which are used to establish the angle automatically and enable the saw to be merely moved across the fence or the like to make the cut. Typically these devices may be heavy and stationary, or complicated by the addition of a number of other functions. A simple device that is integral with the existing carpenter's square, and that would accommodate both left-space and right-space handed carpenters, enabling saw cuts to be made on either leg of the square without visual reference to a pencil line, would be a welcome addition to the options of the carpenter.